Flowmeters such as magnetoinductive flowmeters have been well-known for a long time and are widely employed in a variety of applications. Magnetoinductive flowmeters in particular are used in volumetric filling and metering processes, meaning that magnetoinductive flowmeters are used in conjunction with filling machines for bottling or otherwise packaging liquid foods such as beverages.
The underlying concept of a magnetoinductive flowmeter for flowing media goes all the way back to Faraday who in 1832 suggested using the principle of electromagnetic induction for flow-rate measurements. According to Faraday's law of induction, a flowing medium that contains charge carriers and travels through a magnetic field will generate an electric field intensity perpendicular to the flow direction and to the magnetic field. A magnetoinductive flowmeter utilizes Faraday's law of induction in that a field coil generates a magnetic field with a magnetic field component that extends in a direction perpendicular to the flow path. Within that magnetic field, each volume element of the flowing medium traveling through the magnetic field and containing a certain number of charge carriers contributes the field intensity produced in that volume element to a measuring voltage that can be collected via measuring electrodes.
In conventional magnetoinductive flowmeters, the measuring electrodes are designed either for conductive or for capacitive coupling with the flowing medium. One salient feature of magnetoinductive flowmeters is the proportionality between the measured voltage and the flow rate of the medium averaged across the diameter of the measuring tube, i.e. between the measured voltage and the volume flow.
In the area of the measuring electrodes at a minimum, the interior of the measuring tube must be electrically insulating or lined with an electrically insulating material. In particular, the measuring tube may be produced from a ceramic material in which the measuring electrodes are embedded for instance by a sintering process.
The use of a magnetoinductive flowmeter with a filling machine serving for the bottling or canning of liquid foods is contingent on two prerequisites of great significance: First, hygienic requirements must be met, meaning that the conduits and couplings as well as the junctions between the individual components must be in compliance with hygienic standards. Second, a magnetoinductive flowmeter intended for use with a filling machine must be sufficiently compact, allowing the filling machine to be equipped in space-saving fashion with a large number of these magnetoinductive flowmeters.